Abstract: In the prior funding cycle, we successfully obtained a mechanistic understanding of the chemical basis for the excellent therapeutic actions in mild traumatic brain injury (TBI) of our carbon nanoparticle (CNP) platform, poly(ethylene)glycol-hydrophilic carbon clusters (PEG-HCCs). We identified new actions that point to profound new directions for our CNPs. We: 1) discovered that the HCC's broad redox potential extended their action as a redox mediator among mitochondrial constituents involved in electron transport, i.e. a nanoparticle enzyme, or ?nanozyme?, and 2) identified a new mechanism by which hemorrhage causes cellular toxicity: rapid and persistent generation of DNA double strand breaks and robust DNA damage response leading to cellular ?senescence?, in which cells become a nidus for inflammation. While senescence could be prevented by PEG- HCCs, the cells became sensitized to iron toxicity/ferroptosis. This interaction led us to generate a new CNP, covalently bonding iron chelator, deferoxamine (DEF). Our results indicate DEF-HCC-PEG effectively addressed hemin and iron-related injury, senescence and ferroptosis. Given that mitochondrial dysfunction and hemorrhagic contusion (HC) are associated with poor outcome in TBI, these findings directly indicate the benefit of pursuing these mechanisms. The identification of key mechanistic features of our CNP platform that facilitate a mitochondrial site of action and new mechanism of hemorrhage-induced pathology form the basis for this renewal application. We will incorporate our understanding of the PEG-HCC mechanisms of action to generate a more immediately translatable CNP utilizing a good manufacturing practice (GMP) starting material, activated charcoal, and test them in-vivo in a rodent TBI with hemorrhagic contusion (TBI/HC). Our overall hypothesis is that the mechanisms of action discovered in our prior application will be translatable to GMP starting materials and will act on both the genomic and mitochondrial damage associated with TBI/HC. Specific Aim 1 will test the hypothesis that an oxidizing synthesis environment can be optimized to generate GMP-derived starting materials, PEG-oxidized activated charcoal achieving, the desired characteristics of a CNP nanozyme. Specific Aim 2 will test the hypothesis that DEF-linked CNP will address hemorrhage-related mitochondrial and genomic events triggering senescence and resistance to ferroptosis. Specific Aim 3 will administer the CNPs developed in Aims 1 and 2 to moderate-severe TBI/HC model. Completion of these Aims will yield a more readily translatable version of our CNP platform building on a growing understanding of the critical features and sites of action for their nanozyme mechanisms. New therapeutic targets emerging from a more thorough understanding of pathological mechanisms by which hemorrhage complicates outcome from TBI will guide the design. By employing GMP starting material, this project can generate breakthrough materials more rapidly translatable to the clinic. Because mitochondrial dysfunction and the cellular consequence of hemorrhage are features both of acute injury and of aging and cognitive decline, a broader potential for this therapy is suggested.